Sanitary ware and process for producing the same

ABSTRACT

Sanitary wares having a controlled surface are disclosed which are less likely to be stained or soiled and/or possess excellent gloss. The first sanitary ware comprises a sanitary ware body and a surface glaze layer provided on the sanitary ware body, wherein the surface glaze layer has a center line average roughness Ra of less than 0.07 μm. This sanitary ware is advantageous in that stains or soils are much less likely to be adhered to the surface thereof and, even when adhered to the surface thereof, can be removed by a weak water stream. The second sanitary ware comprises a sanitary ware body and a surface glaze layer provided on the sanitary ware body, wherein the surface glaze layer has a kurtosis Rku of less than 2.70. This sanitary ware advantageously possesses excellent surface gloss. The third sanitary ware comprises a sanitary ware body and a surface glaze layer provided on the sanitary ware body, wherein the surface of the surface glaze layer consists essentially of a vitreous component and is free from silica particles having a particle diameter of not less than 10 μm. This sanitary ware is advantageous in that stains or soils are less likely to be adhered to the surface thereof.

This application claims the benefit of and is a continuation ofInternational Application No. PCT/JP99/02810, which has theinternational filing date of May 27, 1999, and which was not publishedunder PCT Article 21(2) in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to sanitary wares, such as toilets,urinals, strainers for urinals, flush tanks for toilets or urinals,washbowls in washstands, or wash hand basins, and a process forproducing the same.

2. Background Art

Good appearance and high cleanness are important for the surface ofsanitary wares from the viewpoints of hygiene and aesthetic effect.Further, retention of good appearance and high cleanness for a longperiod of time is preferred.

In order to keep the surface of sanitary wares clean and to retain goodappearance of the surface of sanitary wares, it is a common practice tostrongly scrub the surface thereof by a scrubbing brush or a cleaningbrush containing a detergent, such as a surfactant, an acid detergent,or an alkali detergent. Specifically, stains or soils deposited on thesurface of sanitary wares are removed through utilization of chemicaldetergency derived from the detergent and through utilization ofphysical cleaning action by scrubbing with the scrubbing brush or thecleaning brush.

This cleaning work is not light, and, hence, reducing the frequency ofthe cleaning work is desired. Further, in recent years, environmentalpollution by surfactant-containing wastewater has been pointed out.Therefore, reducing the amount of the surfactant used and the frequencyof use of the surfactant is desired.

Under these circumstances, several proposals have been made on sanitarywares having a surface that is highly hygienic and has good appearance.

For example, coating of a fluororesin or a siloxane resin containingfluoroalkyl groups onto the surface of sanitary ware has been proposedto lower the surface energy, thereby permitting stains or soils to beless likely to be deposited onto the surface.

Another proposal is such that the surface of sanitary ware is madesmooth as much as possible to prevent stains or soils from beingdeposited and strongly adhered onto the surface thereof. In thisproposal, however, the relationship of the surface state to theinhibition of deposition of stains or soils, fastness, and glossinesshas not been fully studied. Specifically, the sanitary ware having asmooth surface has been proposed based on such mere conceptualunderstanding that a smooth surface would inhibit the deposition ofstains or soils thereon and would be preferred from the viewpoint ofaesthetic effect.

SUMMARY OF THE INVENTION

The present inventors have now found that control of the surface stateof a glaze layer can provide sanitary wares that are less likely to bestained and soiled and/or possess excellent gloss.

Accordingly, it is an object of the first aspect of the presentinvention to provide a sanitary ware that is less likely to be stainedand soiled on the surface thereof and, upon deposition of stains orsoils on the surface thereof, permits the stains or soils to be removedby a weak stream of water.

It is an object of the second aspect of the present invention to providea sanitary ware that possesses excellent surface gloss.

It is an object of the third aspect of the present invention to providea sanitary ware that is less likely to be stained and soiled.

According to the first aspect of the present invention, there isprovided a sanitary ware comprising: a sanitary ware body; and a surfaceglaze layer provided on the sanitary ware body, the surface glaze layerhaving a center line average roughness Ra of less than 0.07 μm asmeasured with a stylus type surface roughness tester according to JIS B0651-1996.

According to the second aspect of the present invention, there isprovided a sanitary ware comprising: a sanitary ware body; and a surfaceglaze layer provided on the sanitary ware body, the surface glaze layerhaving a kurtosis Rku of less than 2.70.

According to the third aspect of the present invention, there isprovided a sanitary ware comprising: a sanitary ware body; and a surfaceglaze layer provided on the sanitary ware body, the surface of thesurface glaze layer consisting essentially of a vitreous component and,in addition, being free from silica particles having a size of not lessthan 10 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged diagram showing the state of the surface ofearthenware in Comparative Example A1 as measured with a stylus typesurface roughness tester (JIS B 0651), wherein numeral 1 designates acenter line and numeral 2 the surface of a glaze layer;

FIG. 2 is an enlarged diagram showing the state of the surface ofearthenware in Comparative Example A2 as measured with a stylus typesurface roughness tester (JIS B 0651), wherein numeral 1 designates acenter line and numeral 2 the surface of a glaze layer;

FIG. 3 is an enlarged diagram showing the state of the surface ofearthenware in Example A1 as measured with a stylus type surfaceroughness tester (JIS B 0651), wherein numeral 1 designates a centerline and numeral 2 the surface of a glaze layer;

FIG. 4 is an enlarged diagram showing the state of the surface ofearthenware in Example A3 as measured with a stylus type surfaceroughness tester (JIS B 0651), wherein numeral 1 designates a centerline and numeral 2 the surface of a glaze layer;

FIG. 5 is an enlarged diagram showing the state of the surface ofearthenware in Example A6 as measured with a stylus type surfaceroughness tester (JIS B 0651), wherein numeral 1 designates a centerline and numeral 2 the surface of a glaze layer;

FIG. 6 is an enlarged diagram showing the state of the surface ofearthenware in Example A7 as measured with a stylus type surfaceroughness tester (JIS B 0651), wherein numeral 1 designates a centerline and numeral 2 the surface of a glaze layer;

FIGS. 7(a) and 7(b) are reflection electron photomicrographs of thesurface of earthenware in Comparative Example A1 observed under ascanning electron microscope, wherein 7(a) shows an concave-convex imageof the surface and 7(b) an image on the composition of the surface;

FIGS. 8(a) and 8(b) are a reflection electron photomicrographs of thesurface of earthenware in Example A1 observed under a scanning electronmicroscope, wherein 8(a) shows an concave-convex image of the surfaceand 8(b) an image on the composition of the surface;

FIG. 9 is a diagram showing the state of the surface of earthenware inComparative Example A1 obtained by observation under an atomic forcemicroscope;

FIG. 10 is a diagram showing the state of the surface of earthenware inComparative Example A2 obtained by observation under an atomic forcemicroscope;

FIG. 11 is a diagram showing the state of the surface of earthenware inExample A1 obtained by observation under an atomic force microscope;

FIG. 12 is a diagram showing the state of the surface of earthenware inExample A2 obtained by observation under an atomic force microscope;

FIG. 13 is a diagram showing the state of the surface of earthenware inExample A3 obtained by observation under an atomic force microscope;

FIG. 14 is a diagram showing the state of the surface of earthenware inExample A5 obtained by observation under an atomic force microscope;

FIG. 15 is a graph showing the relationship between kurtosis Rku andglossiness Gs (60°) in Example B and Comparative Example B;

FIG. 16 is a reflection electron image of the glaze surface before analkali resistance test in Comparative Example C2 observed under ascanning electron microscope;

FIG. 17 is a reflection electron image of the glaze surface after analkali resistance test in Comparative Example C2 observed under ascanning electron microscope;

FIG. 18 is a reflection electron image of the glaze surface before analkali resistance test in Example C2 observed under a scanning electronmicroscope;

FIG. 19 is a reflection electron image of the glaze surface after analkali resistance test in Example C2 observed under a scanning electronmicroscope;

FIG. 20 is a reflection electron image of the glaze surface before analkali resistance test in Comparative Example D1 observed under ascanning electron microscope;

FIG. 21 is a reflection electron image of the glaze surface after analkali resistance test in Comparative-Example D1 observed under ascanning electron microscope;

FIG. 22 is a reflection electron image of the glaze surface before analkali resistance test in Example D1 observed under a scanning electronmicroscope;

FIG. 23 is a reflection electron image of the glaze surface after analkali resistance test in Example D1 observed under a scanning electronmicroscope; and

FIG. 24 is a schematic diagram showing a stylus type surface roughnesstester according to JIS B 0651-1996.

DETAILED DESCRIPTION OF THE INVENTION Definition

The term “sanitary ware” used herein refer to earthenware products usedin or around lavatories and washrooms, and specific examples thereofinclude toilets, urinals, strainers for urinals, flush tanks for toiletsor urinals, washbowls in washstands, and wash hand basins.

The term “earthenware” used herein refers to a ceramic ware the body ofwhich has been densified to such an extent that the body has slightwater absorption, the ceramic ware having a glazed surface.

The particle diameter obtained by particle size distribution measurementaccording to laser diffractometry, for example “50% particle diameter,”refers to a particle diameter when the accumulated number of fineparticles counted from the finer particle side in measured data onparticle size distribution measured by laser diffractometry has reached50% of the particles. In the following description, the particlediameter referred to together with the “50% particle diameter” or“particle diameter of D50” means “50% particle diameter” obtained byparticle size distribution measurement according to laserdiffractometry.

Sanitary Ware According to First Aspect of the Invention

The sanitary ware according to the first aspect of the present inventioncomprises: a sanitary ware body; and a surface glaze layer provided onthe sanitary ware body, the surface glaze layer having a center lineaverage roughness Ra of less than 0.07 μm. According to a preferredembodiment of the present invention, the center line average roughnessRa is preferably not more than 0.068 μm, more preferably not more than0.05 μm, most preferably not more than 0.03 μm. So far as the presentinventors know, no product having a surface roughness controlled to theabove range has hitherto been proposed in sanitary ware fields, and thesurface roughness Ra of commercially available products is about 0.1 μmat best.

According to the sanitary ware of the present invention, urinaryclaculi, mold, materials, which render the surface of the sanitary wareyelowish, and other stains or soils are less likely to be deposited onthe surface thereof, and, even when deposited on the surface, can beremoved by a weak stream of water. As a result, the surface of thesanitary ware can be kept clean for a long period of time withoutfrequent water flushing. It has been known that stains or soils are lesslikely to be deposited on a smooth surface. The effect of the presentinvention is surprisingly much better than that expected from theconventional finding. For example, as is apparent from working examplesdescribed below, according to the sanitary ware of the presentinvention, smears of a marking ink (Magic™ ink), upon contact withwater, are floated on water, and can be removed by running water. Thisis true of a salad oil. Further, scale and urinary calculi are much lesslikely to be deposited, and, even when deposited on the surface of thesanitary ware, can be easily removed. The high level of inhibition ofthe deposition of stains or soils on the surface of the sanitary wareand the high removability of stains and soils are utterly unexpected andanticipated from the conventional finding. The above effect issignificant when the center line average roughness is in the aboverange. When the center line average roughness is outside the aboverange, the effect is significantly lost. That is, the above center lineaverage roughness range is critical for attaining the above significanteffect.

Although the reason why the effect of the present invention can beattained has not been fully elucidated yet, it is believed as follows.The area of contact between stains or soils and the surface isconsidered to decrease with increasing the smoothness of the surface.Consequently, the adhesion between the surface and the stains or soilsis considered to decrease with increasing the smoothness of the surface.In this case, when the stains or soils are surrounded by water, asmoother surface having a lower adhesion to the stains or soils permitsstains or soils to be more easily floated on and removed by water,because buoyancy acting on the stains or soils is proportional to thesize of the stains or soil. This way of thinking is an extension of theconventional finding, and is unsatisfactory for explaining thecriticality of the center line average roughness range for attaining theeffect of the present invention. In the present invention, it isestimated that, when the level of the smoothness (center line averageroughness) is in the above range, a great change occurs in interactionbetween the stains or soils and the glaze surface. This, however, ismere estimation, and the present invention is not limited to this way ofthinking.

The “center line average roughness or roughness average Ra” means thevalue obtained by the following formula and expressed in micrometer (m)when sampling only the reference length from the roughness curve in thedirection of mean line, taking X-axis in the direction of mean line andY-axis in the direction of longitudinal magnification of this sampledpart and the roughness curve is expressed by Y=f(x):

 R _(n)=1/l∫ ^(f) ₀|∫(x)|dx

wherein represents reference length).

In the present invention, the center line average roughness Ra is inaccordance with the definition and designation specified in JIS B0601-1994 and measured with a stylus type surface roughness testeraccording to JIS B 0651-1996. These JIS, together with Englishtranslation thereof, are easily available from Japanese StandardsAssociation (1-24, Akasaka 4-chome, Minato-ku, Tokyo, Japan), and areincorporated herein by reference.

The roughness tester is schematically shown in FIG. 24. In the drawing,a detector 11 comprises a stylus 12 and a skid 13. The detector 11detects displacement in the vertical direction, while it is traveled onthe surface of a sample 14 put on a fixing jig 15 by means of feedingdevice 16. This displacement is passed through a magnifying device (notshown), and displayed on an indicator or a recorder to obtain a surfaceroughness curve.

The present inventors have found that a preferred formulation and a morepreferred formulation of the glaze are as follows, although the effectof the present invention does not greatly depend upon the composition ofthe glaze.

Formulation, wt % Preferred range More preferred range SiO₂: 55 to 80 60to 80 Al₂O₃:  5 to 13  5 to 10 Fe₂O₃: 0.1 to 0.4 0.1 to 0.4 MgO: 0.8 to3.0 0.8 to 3.0 CaO:  8 to 17  8 to 15 ZnO: 3 to 8 4 to 8 K₂O: 1 to 4 1to 4 Na₂O: 0.5 to 2.5 0.5 to 2.5 ZrO₂: 0.1 to 15  0.1 to 15  Pigment:  1to 20  1 to 20

According to a preferred embodiment of the present invention, anadditional function can be imparted to the glaze layer by addingadditives, other than the glaze, to the glaze layer. In this case,additives, which may be preferably added to the glaze, are such thatthey are reacted with the glaze or the atmosphere within the kiln duringfiring to form a compound. For example, antimicrobial effect can beprovided, for example, by the addition of antimicrobial metals, such assilver, copper, zinc, or compounds and solid solutions thereof, andphotocatalysts, such as titanium oxide, zinc oxide, tin oxide, ferricoxide, tungsten trioxide, strontium titanate, and dibismuth trioxide.Further, the presence of the photocatalyst can also offer photoreductioneffect that can promote hydrophilification.

According to the present invention, the thickness of the surface glazelayer may be properly determined. For example, the thickness isgenerally about 0.1 to 3 mm, preferably about 0.2 to 2 mm, morepreferably 0.3 to 1.2 mm.

According to a preferred embodiment of the present invention, thesurface glaze layer is absent on a part of the surface of the sanitaryware according to the present invention. The sanitary ware according tothe present invention is preferably produced by a production processdescribed below. In this case, gases evolved during firing are releasedthrough portions not provided with the glaze layer. This can effectivelyprevent gases from being introduced into and stayed in the glaze layer,and hence can effectively prevent the occurrence of poor appearance.This embodiment is particularly advantageous when firing is carried outat a time after coating of a glaze material onto the sanitary ware body.

According to another embodiment of the present invention, a glaze layeris provided between the sanitary ware body and the surface glaze layer.In this case, the glaze layer may have a multi-layer structure so far asthe surface of the surface glaze layer as the outermost layer has Rafalling within the above defined range. More specifically, according toa preferred embodiment of the present invention, a color glaze layer isprovided between the sanitary ware body and the surface glaze layer, andthe surface glaze layer is transparent. According to this embodiment,the thickness of the surface glaze layer may be reduced, and even whenthe surface glaze layer has become very soft during firing, it ispossible to effectively prevent such an unfavorable phenomenon thatgases enter and are stayed in the glaze layer and consequently createpoor appearance. Further, when zinc is contained as the glaze component,the zinc component is vaporized during firing, and deposited as zincflowers within a kiln, resulting in contamination of the firing kiln.When the surface glaze layer is provided, however, zinc vaporized in theglaze layer as the intermediate layer cannot be introduced into theatmosphere within the kiln without passage through the surface glazelayer. Therefore, when the glaze layer is formed so as to have atwo-layer structure with the total thickness of the two layers beingequal to the thickness of the glaze layer formed in a single layerstructure, the contamination of the kiln with zinc flowers can be morefully inhibited as compared with the provision of the glaze layer in asingle layer structure, that is, the provision of the surface glazelayer alone as the glaze layer. Further, zinc is concentrated on thesurface so that the concentration of zinc in the composition isgradually increased toward the surface, leading to an advantage that theantimicrobial activity is exhibited for a long period of time. Alsoaccording to this embodiment, as described above, preferably, the glazelayer is absent on a part of the sanitary ware.

According to another preferred embodiment of the present invention, thecontact angle of the surface glaze layer in the sanitary ware of thepresent invention with water is preferably less than 30°, morepreferably not more than 25°, most preferably not more than 20°. In thiscase, by virtue of the hydrophilic nature of the surface glaze layer,stains and soils are less likely to be deposited, and, even whendeposited on the surface thereof, can be easily removed. Thus, theeffect of the present invention can be attained on a higher level.

As described above, the sanitary ware according to the present inventionis specifically in the form of toilets, urinals, strainers for urinalsand the like. In the toilets and urinals, the deposition of materials,which render the surface thereof yellowish, and the like onto the bowlportion or the trap portion can be effectively prevented, and, eventhough these material are once deposited, they can be easily removed.Further, the sanitary ware according to the present invention may be inthe form of washbowls in washstands. In washbowls, the deposition ofsoap soils, scale soils and the like can be effectively prevented, and,even though these soils are once deposited, they can be easily removed.

According to a preferred embodiment of the present invention, thesanitary ware of the present invention can be produced by providing anyone of the following glaze materials for a surface glaze layer, applyingthe glaze material on a sanitary ware body, and firing the sanitary warebody with the glaze material applied thereon:

(1) a glaze material having a 50% particle diameter (D50) of 1.5 μm asdetermined by particle size distribution measurement according to laserdiffractometry;

(2) an amorphous glaze material such as a vitrified frit glaze material;and

(3) a mixed glaze comprised of an amorphous glaze material such as avitrified frit glaze material and a non-frit glaze material.

The sanitary ware body may be any conventional sanitary ware body whichis prepared, for example, by properly shaping a slurry for a sanitaryware body obtained using quartz sand, feldspar, clay and the like as rawmaterials.

The glaze material (1) may be provided by grinding the glaze materialpowder by means of a ball mill or the like. Use of the ground glazematerial can provide a sanitary ware having a smooth surface accordingto the present invention.

The amorphous glaze material such as the vitrified frit glaze material(2) may be obtained by melting a glaze material powder at a hightemperature of 1300° C. or above. Use of the previously vitrified glazematerial can provide a sanitary ware having a smooth surface accordingto the present invention.

The glaze material (3) is a mixture of an amorphous glaze material suchas a vitrified frit glaze material with a non-frit glaze material. Theamorphous glaze material may be obtained in the same manner as describedabove in connection with the glaze material (2).

The particle diameter of the non-frit glaze material powder is notparticularly limited. However, the smaller the particle diameter of thenon-frit glaze material, the better the results. More specifically, the50% particle diameter of the non-frit glaze material is preferably notmore than 6 μm, more preferably not more than 4 μm, particularlypreferably not more than 1.5 μm.

According to a preferred embodiment of the present invention, in theglaze material (3), at least silica particles in the glaze materialpowder have been subjected to size reduction to a 50% particle diameterof not more than 6 μm, more preferably not more than 4 μm. According tothis embodiment, the amount of silica particles remaining unreacted onthe surface after firing can be reduced. The present inventors havefound that, when the sanitary ware is a toilet or a urinal which is usedin an environment exposed to an alkali solution (an ammonia-containingsolution), portions around the silica particles are preferentiallydeteriorated, resulting in lowered smoothness of the surface. Morespecifically, silica particles or zircon particles left on the glazesurface after firing constitute irregularities on the surface. It wasfound that sites around the silica particles or zircon particlesconstituting the irregularities are preferentially deteriorated in avery short period of about two months under an alkaline environment. Thecreation of irreguralities can be effectively prevented by controllingthe diameter of the silica particles. This can offer an advantage thatthe alkali resistance of the surface glaze layer is significantlyimproved.

According to a preferred embodiment of the present invention, in theglaze material (3), when the non-frit glaze material has not beensatisfactorily subjected to size reduction, for example, has a 50%particle diameter of about 6 m, the content of the amorphous glazematerial such as the frit glaze material in the mixed glaze ispreferably not more than 50% by weight, more preferably not more than30% by weight. This can prevent gases evolved during firing from beingstayed in the glaze layer and hence can prevent the occurrence of poorappearance.

In some cases, preferably, the frit glaze material has a softeningtemperature above that of the non-frit glaze material powder. This alsocan prevent gases evolved during firing from being stayed in the glazelayer and hence can prevent the occurrence of poor appearance.

The glaze material may be applied to the sanitary ware body by anymethod without particular limitation, and a conventional method may beproperly selected from spray coating, dip coating, spin coating, rollcoating and the like.

The sanitary ware body with the precursor layer for a surface glazelayer being formed thereon is then fired. The firing temperature mayvary depending upon whether or not the sanitary ware body has beenpreviously sintered. When the ware body has not been previouslysintered, firing is preferably carried out at a temperature of 1000° C.or above which causes sintering of the ware body and softening of theglaze. On the other hand, when the ware body has been previouslysintered, firing is preferably carried out at a temperature of 300° C.or above, more preferably 400° C. or above, which can soften the glaze.The former method, that is, a method wherein, after a glaze material iscoated onto the unsintered ware body, firing is carried out at a time,is preferred from the viewpoint of the production cost of the sanitaryware.

On the other hand, the latter method is advantageous in that theformation of a surface glaze layer on the completed sanitary ware canimpart a new function.

The sanitary ware comprising an additional glaze layer between thesanitary ware body and the surface glaze layer may be produced in thesame manner as described above, except that the step of forming aprecursor layer for the glaze layer as the intermediate layer is added.Specifically, this sanitary ware may be produced in the same manner asdescribed above, except that a precursor layer for the glaze layer asthe intermediate layer, for example, a precursor for a color glaze layeris formed and a precursor for the surface glaze layer is formed thereonfrom any one of the glaze materials (1) to (3).

In this case, the thickness of the surface glaze layer is generally 0.05to 1.2mm, preferably 0.1 to 0.8mm, more preferably 0.15 to 0.4 mm. Thethickness of the color glaze layer is generally 0.05 to 1.8 mm,preferably 0.1 to 1.2 mm, more preferably 0.2 to 0.7 mm.

According to a preferred embodiment of the present invention, when thecolor glaze layer is formed between the sanitary ware body and thesurface glaze layer, the D50 of the glaze material capable of formingthe color glaze layer is preferably not less than 4 μm. A combination ofthe use of the color glaze material having such a particle diameter withthe use of any one of the glaze materials (1) to (3) can prevent gasesevolved during firing from being stayed in the glaze layer and hence canprevent the occurrence of poor appearance.

Further, according to a preferred embodiment of the first aspect of thepresent invention, when the color glaze layer is formed between thesanitary ware body and the surface glaze layer, the use of the mixedglaze (3) is preferred. More preferably, the mixed glaze (3) used issuch that the non-frit glaze material has been subjected to sizereduction to a 50% particle diameter of not more than 6 μm and is freefrom a pigment and/or an emulsifier (specifically ZrO₂). In this case,50 to 99% by weight, preferably 60 to 95% by weight, of the mixed glazeis accounted for by the frit glaze material. Most preferably, the ratioof the non-frit glaze material to the frit glaze material is 30:70 to10:90. In this case, the firing temperature is preferably 800 to 1300°C. In summary, the preferred production process comprises the steps of:applying a color glaze material with a pigment and an emulsifier addedthereto onto a sanitary ware body; further applying a mixed glaze,prepared by mixing a transparent non-frit glaze material containingneither a pigment nor an emulsifier with 50 to 99% by weight, preferably60 to 90% by weight, of a frit glaze; and then conducting firing at atemperature of 800 to 1300° C.

Sanitary Ware According to Second aspect of the Invention

The sanitary ware according to the second aspect of the presentinvention comprises: a sanitary ware body; and a surface glaze layerprovided on the sanitary ware body, the surface glaze layer having akurtosis Rku of less than 2.70, preferably not more than 2.6, morepreferably not more than 2.50.

The sanitary ware according to the second aspect of the presentinvention has excellent surface gloss.

According to the present invention, the kurtosis Rku is defined asfollows. Specifically, the kurtosis Rku is determined from Y=f(x) in theroughness curve explained above in connection with the first embodimentby the following equation:${Rq} = \sqrt{\frac{1}{l}{\int_{0}^{l}{{{f(x)}}^{2}{x}}}}$

The kurtosis Rku is a parameter for quantitatively expressing theacuteness of an amplitude distribution curve and can be determined bythe following equation:${Rku} = {\frac{1}{{LRq}^{4}}{\int_{0}^{l}{{{f(x)}}^{4}{x}}}}$

As with the sanitary ware according to the first aspect of the presentinvention, the sanitary ware according to the second aspect of thepresent invention may be in the form of toilets, urinals, strainers forurinals, washbowls in washstands and the like. In the sanitary wareaccording to the second aspect of the present invention, the compositionof the glaze layer, the thickness thereof, other preferred embodimentsand the production process thereof, may be the same as described abovein connection with the first aspect of the present invention.

The present inventors have found that a preferred formulation and a morepreferred formulation of the glaze are as follows, although the effectof the present invention does not greatly depend upon the composition ofthe glaze.

Formulation, wt % Preferred range More preferred range SiO₂: 55 to 80 60to 80 Al₂O₃:  5 to 13  5 to 10 Fe₂O₃: 0.1 to 0.4 0.1 to 0.4 MgO: 0.8 to3.0 0.8 to 3.0 CaO:  8 to 17  8 to 15 ZnO: 3 to 8 4 to 8 K₂O: 1 to 4 1to 4 Na₂O: 0.5 to 2.5 0.5 to 2.5 ZrO₂: 0.1 to 15  0.1 to 15  pigment:  1to 20  1 to 20

According to a preferred embodiment of the present invention, anadditional function can be imparted to the glaze layer by addingadditives, other than the glaze, to the glaze layer. In this case,additives, which may be preferably added to the glaze, are such thatthey are reacted with the glaze or the atmosphere within the kiln duringfiring to form a compound. For example, antimicrobial effect can beprovided, for example, by the addition of antimicrobial metals, such assilver, copper, zinc, or compounds and solid solutions thereof, andphotocatalysts, such as titanium oxide, zinc oxide, tin oxide, ferricoxide, tungsten trioxide, strontium titanate, and dibismuth trioxide.Further, the presence of the photocatalyst can also offer photoreductioneffect that can promote hydrophilification.

According to the present invention, the thickness of the surface glazelayer may be properly determined. For example, the thickness isgenerally about 0.1 to 3 mm, preferably about 0.2 to 2 mm, morepreferably 0.3 to 1.2 mm.

According to a preferred embodiment of the present invention, thesurface glaze layer is absent on a part of the surface of the sanitaryware according to the present invention. The sanitary ware according tothe present invention is preferably produced by a production processdescribed below. In this case, gases evolved during firing are releasedthrough portions not provided with the glaze layer. This can effectivelyprevent gases from being introduced into and stayed in the glaze layer,and hence can effectively prevent the occurrence of poor appearance.This embodiment is particularly advantageous when firing is carried outat a time after coating of a glaze material onto the sanitary ware body.

According to another embodiment of the present invention, a glaze layeris provided between the sanitary ware body and the surface glaze layer.In this case, the glaze layer may have a multi-layer structure so far asthe surface of the surface glaze layer as the outermost layer has Rkufalling within the above defined range. More specifically, according toa preferred embodiment of the present invention, a color glaze layer isprovided between the sanitary ware body and the surface glaze layer, andthe surface glaze layer is transparent. According to this embodiment,the thickness of the surface glaze layer may be reduced, and even whenthe surface glaze layer has become very soft during firing, it ispossible to effectively prevent such an unfavorable phenomenon thatgases enter and are stayed in the glaze layer and consequently createpoor appearance. Further, when zinc is contained as the glaze component,the zinc component is vaporized during firing, and deposited as zincflowers within a kiln, resulting in contamination of the firing kiln.When the surface glaze layer is provided, however, zinc vaporized in theglaze layer as the intermediate layer cannot be introduced into theatmosphere within the kiln without passage through the surface glazelayer. Therefore, when the glaze layer is formed so as to have atwo-layer structure with the total thickness of the two layers beingequal to the thickness of the glaze layer formed in a single layerstructure, the contamination of the kiln with zinc flowers can be morefully inhibited as compared with the provision of the glaze layer in asingle layer structure, that is, the provision of the surface glazelayer alone as the glaze layer. Further, zinc is concentrated on thesurface so that the concentration of zinc in the composition isgradually increased toward the surface, leading to an advantage that theantimicrobial activity is exhibited for a long period of time. Alsoaccording to this embodiment, as described above, preferably, the glazelayer is absent on a part of the sanitary ware.

In this case, the thickness of the surface glaze layer is generally 0.05to 1.2 mm, preferably 0.1 to 0.8 mm, more preferably 0.15 to 0.4 mm. Thethickness of the color glaze layer is generally 0.05 to 1.8 mm,preferably 0.1 to 1.2 mm, more preferably 0.2 to 0.7 mm.

According to a preferred embodiment of the present invention, thesanitary ware of the present invention can be produced by providing anyone of the following glaze materials for a surface glaze layer, applyingthe glaze material on a sanitary ware body, and firing the sanitary warebody with the glaze material applied thereon:

(1) a glaze material having a 50% particle diameter (D50) of 1.5 μm asdetermined by particle size distribution measurement according to laserdiffractometry;

(2) an amorphous glaze material such as a vitrified frit glaze material;and

(3) a mixed glaze comprised of an amorphous glaze materila such as avitrified frit glaze material and a non-frit glaze material.

The sanitary ware body may be any conventional sanitary ware body whichis prepared, for example, by properly shaping a slurry for a sanitaryware body obtained using quartz sand, feldspar, clay and the like as rawmaterials.

The glaze material (1) may be provided by grinding the glaze materialpowder by means of a ball mill or the like. Use of the ground glazematerial can provide a sanitary ware having a smooth surface accordingto the present invention.

The amorphous glaze material such as the vitrified frit glaze material(2) may be obtained by melting a glaze material powder at a hightemperature of 1300° C. or above. Use of the previously vitrified glazematerial can provide a sanitary ware having a smooth surface accordingto the present invention.

The glaze material (3) is a mixture of an amorphous glaze material suchas a vitrified frit glaze material with a non-frit glaze material. Theamorphous glaze material may be obtained in the same manner as describedabove in connection with the glaze material (2).

The particle diameter of the non-frit glaze material powder is notparticularly limited. However, the smaller the particle diameter of thenon-frit glaze material, the better the results. More specifically, the50% particle diameter of the non-frit glaze material is preferably notmore than 6 μm, more preferably not more than 4 μm, particularlypreferably not more than 1.5 μm.

According to a preferred embodiment of the present invention, in theglaze material (3), among the components constituting the glaze materialpowder, components, which remain as crystal grains at least afterfiring, have been subjected to size reduction to a 50% particle diameterof not more than 6 μm, more preferably not more than 4 μm. In this case,components, which remain as crystal grains at least after firing, amongthe components constituting the glaze material powder include particlesof pigments, such as zircon, and silica (quartz) particles. The zirconparticles remaining on the glaze surface after firing form dendriformcovexes, and the silica particles remaining on the glaze surface afterfiring forms concaves. In this case, at the firing temperature (800 to1300° C.), the zircon particles remain without dissolution as a solidsolution in the vitreous component in the glaze. On the other hand, thesilica particles are dissolved in the vitreous component in the glazefrom the surface of the particles to form a solid solution . In thiscase, when the particles are coarse, the dissolution in the vitreouscomponent to form a solid solution is unsatisfactory, and the particlesremain without dissolution. Therefore, for particles of both the zirconand the silica, a smaller diameter of the particles can provide betterresults, because the irregularities are reduced.

Further, for the silica particles, fine particles of silica arepreferred because they can contribute to improved alkali resistance and,during use for a long period of time, are less likely to cause anincrease in surface roughness.

According to a preferred embodiment of the present invention, in theglaze material (3), when the non-frit glaze material has not beensatisfactorily subjected to size reduction, for example, has a 50%particle diameter of about 6 μm, the content of the frit glaze materialin the mixed glaze is preferably not more than 50% by weight, morepreferably not more than 30% by weight. This can prevent gases evolvedduring firing from being stayed in the glaze layer and hence can preventthe occurrence of poor appearance.

In some cases, preferably, the amorphous glaze material such as the fritglaze material has a softening temperature above that of the non-fritglaze material powder. This also can prevent gases evolved during firingfrom being stayed in the glaze layer and hence can prevent theoccurrence of poor appearance.

The glaze material may be applied to the sanitary ware body by anymethod without particular limitation, and a conventional method may beproperly selected from spray coating, dip coating, spin coating, rollcoating and the like.

The sanitary ware body with the precursor layer for a surface glazelayer being formed thereon is then fired. The firing temperature mayvary depending upon whether or not the sanitary ware body has beenpreviously sintered. When the ware body has not been previouslysintered, firing is preferably carried out at a temperature of 1000° C.or above which causes sintering of the ware body and softening of theglaze. On the other hand, when the ware body has been previouslysintered, firing is preferably carried out at a temperature of 300° C.or above, more preferably 400° C. or above, which can soften the glaze.The former method, that is, a method wherein, after a glaze material iscoated onto the unsintered ware body, firing is carried out at a time,is preferred from the viewpoint of the production cost of the sanitaryware.

On the other hand, the latter method is advantageous in that theformation of a surface glaze layer on the completed sanitary ware canimpart a new function.

The sanitary ware comprising an additional glaze layer between thesanitary ware body and the surface glaze layer may be produced in thesame manner as described above, except that the step of forming aprecursor layer for the glaze layer as the intermediate layer is added.Specifically, this sanitary ware may be produced in the same manner asdescribed above, except that a precursor layer for the glaze layer asthe intermediate layer, for example, a precursor for a color glaze layeris formed and a precursor for the surface glaze layer is formed thereonfrom any one of the glaze materials (1) to (3).

According to a preferred embodiment of the present invention, when thecolor glaze layer is formed between the sanitary ware body and thesurface glaze layer, the D50 of the glaze material capable of formingthe color glaze layer is preferably not less than 4 μm. A combination ofthe use of the color glaze material having such a particle diameter withthe use of any one of the glaze materials (1) to (3) can prevent gasesevolved during firing from being stayed in the glaze layer and hence canprevent the occurrence of poor appearance.

Sanitary Ware According to the Third Aspect of the Invention

The sanitary ware according to the third aspect of the present inventioncomprises: a sanitary ware body; and a surface glaze layer provided onthe sanitary ware body, the surface of the surface glaze layerconsisting essentially of a vitreous component and, in addition, beingfree from silica particles having a particle diameter of not less than10 μm.

The sanitary ware according to the third aspect of the present inventionpossesses excellent alkali resistance, and, by virtue of the excellentalkali resistance, can effectively prevent deposition of stains or soilson the surface thereof and propagation of bacteria for a long period oftime.

The present inventors have experimentally confirmed the following facts.The surface of the sanitary ware has hitherto been recognized as havinga smooth surface as a result of satisfactory vitrification. Unlike thisrecognition, however, silica particles have remained on the surface ofthe sanitary ware without satisfactory vitrification. Further, it hasbeen found that, after firing, these silica particles, together with thevitreous phase around the silica particles, create residual stress andapplication of some external force is likely to create cracking. Use ofthe sanitary ware having cracks under an environment of aqueous ammoniaor under an environment of soapy water have increased cracks and causeddropouts of silica particles due to a dissolution reaction of thevitreous phase under the alkaline environment. It has been confirmedthat the resultant cracks and the concaves formed by the dropouts ofsilica particles serve as hotbeds of bacteria or deposition sites ofstains or soils and accelerate soiling of the sanitary ware and thewashbowl. More specifically, toilets or urinals are always used in suchan environment as will be exposed to urine. Urine is decomposed toammonia through the action of urease, an enzyme possessed by bacteriapresent in toilet or urinal bowls. That is, the toilets and the urinalsare always exposed to an ammoniacal alkaline environment and are used insuch an environment as will cause expansion of cracks, created aroundsilica particles, or dropouts of silica particles. On the other hand,the washbowls are used in such an environment that alkaline soapy wateris splashed. This results in expansion of cracks, created around silicaparticles, or dropouts of silica particles.

The present inventors have now found that staining or soiling causedthrough the above mechanism which is the problem involved in the use ofthe sanitary ware under an alkaline environment can be satisfactorilyprevented by controlling the surface of the surface glaze layer in sucha manner that the surface consists essentially of a vitreous componentand is free from silica particles having a diameter of not less than 10μm.

According to a preferred embodiment of the present invention, the wholesurface glaze layer consists essentially of a vitreous component and isfree from silica particles having a diameter of not less than 10 μm.

As with the sanitary ware according to the first aspect of the presentinvention, the sanitary ware according to the third aspect of thepresent invention may be in the form of toilets, urinals, strainers forurinals, washbowls in washstands and the like.

The present inventors have found that a preferred formulation and a morepreferred formulation of the glaze are as follows, although the effectof the present invention does not greatly depend upon the composition ofthe glaze.

Formulation, wt % Preferred range More preferred range SiO₂: 55 to 80 60to 80 Al₂O₃:  5 to 13  5 to 10 Fe₂O₃: 0.1 to 0.4 0.1 to 0.4 MgO: 0.8 to3.0 0.8 to 3.0 CaO:  8 to 17  8 to 15 ZnO: 3 to 8 4 to 8 K₂O: 1 to 4 1to 4 Na₂O: 0.5 to 2.5 0.5 to 2.5 ZrO₂: 0.1 to 15 0.1 to 15  pigment:  1to 20  1 to 20

According to a preferred embodiment of the present invention, anadditional function can be imparted to the glaze layer by addingadditives, other than the glaze, to the glaze layer. In this case,additives, which may be preferably added to the glaze, are such thatthey are reacted with the glaze or the atmosphere within the kiln duringfiring to form a compound. For example, antimicrobial effect can beprovided, for example, by the addition of antimicrobial metals, such assilver, copper, zinc, or compounds and solid solutions thereof, andphotocatalysts, such as titanium oxide, zinc oxide, tin oxide, ferricoxide, tungsten trioxide, strontium titanate, and dibismuth trioxide.Further, the presence of the photocatalyst can also offer photoreductioneffect that can promote hydrophilification.

According to the present invention, the thickness of the surface glazelayer may be properly determined. For example, the thickness isgenerally about 0.1 to 3 mm, preferably about 0.2 to 2 mm, morepreferably 0.3 to 1.2 mm.

According to a preferred embodiment of the present invention, thesurface glaze layer is absent on a part of the surface of the sanitaryware according to the present invention. The sanitary ware according tothe present invention is preferably produced by a production processdescribed below. In this case, gases evolved during firing are releasedthrough portions not provided with the glaze layer. This can effectivelyprevent gases from being introduced into and stayed in the glaze layer,and hence can effectively prevent the occurrence of poor appearance.This embodiment is particularly advantageous when firing is carried outat a time after coating of a glaze material onto the sanitary ware body.

According to another embodiment of the present invention, a glaze layeris provided between the sanitary ware body and the surface glaze layer.In this case, the glaze layer may have a multi-layer structure so far asthe surface of the surface glaze layer as the outermost layer is freefrom silica particles having a particle diameter of not less than 10 μm.More specifically, according to a preferred embodiment of the presentinvention, a color glaze layer is provided between the sanitary warebody and the surface glaze layer, and the surface glaze layer istransparent. According to this embodiment, the thickness of the surfaceglaze layer may be reduced, and even when the surface glaze layer hasbecome very soft during firing, it is possible to effectively preventsuch an unfavorable phenomenon that gases enter and are stayed in theglaze layer and consequently create poor appearance. Further, when zincis contained as the glaze component, the zinc component is vaporizedduring firing, and deposited as zinc flowers within a kiln, resulting incontamination of the firing kiln. When the surface glaze layer isprovided, however, zinc vaporized in the glaze layer as the intermediatelayer cannot be introduced into the atmosphere within the kiln withoutpassage through the surface glaze layer. Therefore, when the glaze layeris formed so as to have a two-layer structure with the total thicknessof the two layers being equal to the thickness of the glaze layer formedin a single layer structure, the contamination of the kiln with zincflowers can be more fully inhibited as compared with the provision ofthe glaze layer in a single layer structure, that is, the provision ofthe surface glaze layer alone as the glaze layer. Further, zinc isconcentrated on the surface so that the concentration of zinc in thecomposition is gradually increased toward the surface, leading to anadvantage that the antimicrobial activity is exhibited for a long periodof time. Also according to this embodiment, as described above,preferably, the glaze layer is absent on a part of the sanitary ware.

In this case, the thickness of the surface glaze layer is generally 0.05to 1.2 mm, preferably 0.1 to 0.8 mm, more preferably 0.15 to 0.4 mm. Thethickness of the color glaze layer is generally 0.05 to 1.8 mm,preferably 0.1 to 1.2 mm, more preferably 0.2 to 0.7 mm.

Further, according to a preferred embodiment of the present invention,for the surface of the surface glaze layer in the sanitary wareaccording to the third aspect of the present invention, the center lineaverage roughness Ra as defined in the first aspect of the presentinvention is preferably less than 0.07 μm, more preferably not more than0.068 μm, still more preferably not more than 0.05 μm, most preferablynot more than 0.03 μm. Ra falling within the above range can provide asanitary ware onto which stains or soils are much less likely to bedeposited.

According to a preferred embodiment of the present invention, thesanitary ware according to the third aspect of the present invention ispreferably produced by the following production process.

At the outset, the sanitary ware body may be any conventional sanitaryware body which is prepared, for example, by properly shaping a slurryfor a sanitary ware body obtained using quartz sand, feldspar, clay andthe like as raw materials.

Utilization of a glaze having a 90% particle diameter of not more than20 μm, preferably not more than 10 μm, or a glaze having a 50% particlediameter of not more than 5 μm is preferred as the glaze for the surfaceglaze layer. Use of a glaze with the particle diameter falling withinthe above range results in satisfactory vitrification of silicaparticles at a firing temperature of about 1300° C. or below, morespecifically 1100 to 1300° C. and consequently can effectively preventsilica particles having a particle diameter of not less than 10 μm frombeing stayed on the surface. The glaze having the above particlediameter can be obtained by ball milling or beads milling of the glazematerial.

According to another preferred embodiment of the present invention, theglaze is a mixed glaze prepared by mixing silica particles having a 90%particle diameter of not more than 15 μm, preferably not more than 10μm, more preferably not more than 6 μm, or silica particles having a 50%particle diameter of not more than 5 μm, with a glaze material with thesilica component removed therefrom. That is, preferably, the particlediameter of silica particles is controlled separately from other glazematerials.

Use of a glaze with the particle diameter falling within the above rangeresults in satisfactory vitrification of silica particles at a firingtemperature of about 1300° C. or below, more specifically 1100 to 1300°C. and consequently can effectively prevent silica particles having aparticle diameter of not less than 10 μm from being stayed on thesurface. Silica particles having the above diameter can be obtained, forexample, by ball milling or beads milling of a naturally occurringquartz sand or a commercially available feldspar material.

According to a preferred embodiment of the present invention, the glazeis a mixed glaze comprised of an amorphous glaze material such as a fritglaze material and a non-frit glaze material. The frit glaze materialcan be obtained by melting a glaze material comprising quarts sand,feldspar, lime, clay, a pigment and the like at a high temperature of1300° C. or above.

According to a further preferred embodiment of the present invention,the non-frit glaze material in the mixed glaze is a glaze having a 90%particle diameter of not more than 20 μm, preferably not more than 10μm, or a glaze having a 50% particle diameter of not more than 5 μm.

The glaze material may be applied to the sanitary ware body by anymethod without particular limitation, and a conventional method may beproperly selected from spray coating, dip coating, spin coating, rollcoating and the like.

The sanitary ware body with the precursor layer for a surface glazelayer being formed thereon is then fired. The firing temperature mayvary depending upon whether or not the sanitary ware body has beenpreviously sintered. When the ware body has not been previouslysintered, firing is preferably carried out at a temperature of 1000° C.to preferably 1300° C. which causes sintering of the ware body andsoftening of the glaze. On the other hand, when the ware body has beenpreviously sintered, firing is preferably carried out at a temperatureof 300° C. or above, more preferably 400° C. or above, which can softenthe glaze. The former method, that is, a method wherein, after a glazematerial is coated onto the unsintered ware body, firing is carried outat a time, is preferred from the viewpoint of the production cost of thesanitary ware.

On the other hand, the latter method is advantageous in that theformation of a surface glaze layer on the completed sanitary ware canimpart a new function.

The sanitary ware comprising an additional glaze layer between thesanitary ware body and the surface glaze layer may be produced in thesame manner as described above, except that the step of forming aprecursor layer for the glaze layer as the intermediate layer is added.Specifically, this sanitary ware may be produced in the same manner asdescribed above, except that a precursor layer for the glaze layer asthe intermediate layer, for example, a precursor for a color glazelayer, is formed and a precursor for the surface glaze layer is formedthereon from the above glaze material.

Further, according to a preferred embodiment of the third aspect of thepresent invention, when the color glaze layer is formed between thesanitary ware body and the surface glaze layer, the glaze material is amixed glaze composed of the non-frit glaze material and the frit glazematerial. More preferably, the mixed glaze used is such that thenon-frit glaze material has been subjected to size reduction to a 50%particle diameter of not more than 6 μm and is free from a pigmentand/or an emulsifier (specifically ZrO₂). In this case, 50 to 99% byweight, preferably 60 to 95% by weight, of the mixed glaze is accountedfor by the frit glaze material. Most preferably, the ratio of thenon-frit glaze material to the fit glaze material is 30:70 to 10:90. Inthis case, the firing temperature is preferably 1300° C. or below, morespecifically 800 to 1300° C. In summary, the preferred productionprocess comprises the steps of: applying a color glaze material with apigment and an emulsifier added thereto onto a sanitary ware body,further applying a mixed glaze, prepared by mixing a transparentnon-frit glaze material containing neither a pigment nor an emulsifierwith 50 to 99% by weight, preferably 60 to 90% by weight, of a fritglaze; and then conducting firing at a temperature of 1300° C. or below,more specifically 800 to 1300° C.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples, though it is not limited to these examples only.

Example A Composition of Glaze

In the following Example A and Comparative Example A, material A for aglaze has the following composition.

SiO₂: 55 to 80 wt %

Al₂O₃: 5 to 13 wt %

Fe₂O₃: 0.1 to 0.4 wt %

MgO: 0.8 to 3.0 wt %

CaO: 8 to 17 wt %

ZnO: 3 to 8 wt %

K₂O: 1 to 4 wt %

Na₂O: 0.5 to 2.5 wt %

ZrO₂: 0.1 to 15 wt %

Pigment: 1 to 20 wt %

Testing Methods

In the following examples and comparative examples, evaluation testswere carried out by the following methods.

Test 1: Contact Angle with Water

The contact angle of the surface of the sample with water was measuredwith a contact angle goniometer (Model CA-X150, manufactured by KyowaInterface Science Co., Ltd.). More specifically, a water droplet wasdropped on the surface of the sample through a microsyringe and, 30 secafter that, the contact angle was measured with the contact anglegoniometer.

Test 2: Removability of Smears

The inside of a portion having a size of 10 mmφ on the surface of thesample was blotted with an oil-based black marking ink (Magic Ink #700),followed by drying at room temperature for about one min. Thereafter, 3ml of water was dropped on the sample, and the sample was then inspectedon whether or not the Magic Ink was floated, and on whether or not theMagic Ink was washed away upon inclination of the sample.

Test 3: Removability of Oil Stains Under Water

A salad oil (0.01 g) was dropped on the surface of the sample. The wholesample was then submerged in a water tank, and the time taken for thesalad oil deposited on the surface to be floated on the surface of waterwas measured.

Test 4: Deposition of Urinary Calculi

A plate specimen was installed on a trap portion of a stall urinal(U307C) manufactured by TOTO, LTD., and allowed to stand under ordinaryservice conditions for 7 days. Thereafter, the amount of urinary calculideposited on the surface was visually evaluated.

Test 5: Deposition of Soap soils

A plate specimen was installed around a drainage port of a washstandprovided with a liquid soap, and allowed to stand under ordinary serviceconditions for 7 days. Thereafter, the amount of soap soils deposited onthe surface of the specimen was visually evaluated.

Example A1

The material A for a glaze (600 g), 400 g of water, and 1 kg of aluminaballs were placed in a ceramic pot having a volume of 2 liters, and themixture was then ball milled for about 65 hr to obtain a glaze. Theparticle diameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 98% of the particles were accounted for by particles having adiameter of not more than 10 μm and the 50% average particle diameter(D50) was 1.2 μm.

Next, a plate specimen having a size of 70×150 mm was prepared using aslurry for a sanitary ware body obtained using quartz sand, feldspar,clay and the like as raw materials. The glaze was spray coated onto theplate specimen, followed by firing at a temperature of 1300° C. orbelow, more specifically at 1100 to 1200° C., to obtain a sample.

For the sample thus obtained, the center line surface roughness Ra (JISB 0601) was measured with a stylus type surface roughness tester (JIS B0651), and found to be Ra=0.02 μm. Further, the surface roughness of100×100 μm was measured by atomic force microscopy (AFM; Nano Scope III,manufactured by Digital Instruments), and found to be Ra=4.3 μm.

FIG. 3 shows an enlarged view of the surface obtained using the stylustype surface roughness tester. A concave-convex image of the surfaceutilizing a reflection electron image is shown in FIG. 8(a), and animage on the composition of the surface is shown in FIG. 8(b). Further,FIG. 11 is an enlarged view of the surface obtained by observation underan atomic force microscope (AFM).

For the sample, tests 1 to 5 described above were carried out. Theresults were as follows.

Test 1: The contact angle with water was 20°.

Test 2: About 30 sec after dropping of water, the Magic Ink was floatedon the surface of water, and, upon inclination of the sample, the MagicInk, together with water, was washed away to entirely remove the MagicInk on the surface of the sample.

Test 3: 35 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: The amount of urinary calculi deposited was smaller than that inComparative Example A1 described below, and a part of the depositedurinary calculi was washed out by running water.

Test 5: The amount of soap soil deposited was smaller than that inComparative Example A1, and soap soil could be removed by rubbing with awater-containing sponge to expose the original surface of the glazelayer.

Example A2

A material was provided which had the same composition as the material Afor a glaze except that the ZrO₂ component as the emulsifier and thepigment were removed from the composition of the material A for a glaze.This material (600 g), 400 g of water, and 1 kg of alumina balls wereplaced in a ceramic pot having a volume of 2 liters, and the mixture wasthen ball milled for about 65 hr to obtain a glaze. The particlediameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 98% of the particles were accounted for by particles having adiameter of not more than 10 μm and the 50% average particle diameter(D50) was 1.5 μm.

Next, the above glaze was spray coated onto the same plate specimen asused in Example A1, followed by firing at 1100 to 1200° C. to obtain asample. The glaze layer in this sample was transparent.

For the sample thus obtained, the surface roughness was measured in thesame manner as in Example A1, and found to be Ra=0.03 μm as measured bythe stylus method and Ra=3.5 nm as measured by AFM.

FIG. 12 shows an enlarged view of the surface obtained by atomic forcemicroscopy (AFM).

For the sample, tests 1 to 5 described above were carried out. Theresults were as follows.

Test 1: The contact angle with water was 15°.

Test 2: About 20 sec after dropping of water, the Magic Ink was floatedon the surface of water, and, upon inclination of the sample, the MagicInk, together with water, was washed away to entirely remove the MagicInk on the surface of the sample.

Test 3: 15 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: The amount of urinary calculi deposited was smaller than that inComparative Example A1 described below, and a part of the depositedurinary calculi was washed out by running water.

Test 5: The amount of soap soil deposited was smaller than that inComparative Example A1 described below, and soap soil could be removedby rubbing with a water-containing sponge to expose the original surfaceof the glaze layer.

Example A3

The material A for a glaze was melted at 1300 to 1450° C. in an electricfurnace, and the melt was then quenched in water to obtain a glass frit.The glass frit was then stamp milled. The powder thus obtained (600 g),400 g of water, and 1 kg of alumina balls were placed in a ceramic pothaving a volume of 2 liters, and the mixture was then ball milled forabout 18 hr to obtain a frit glaze. The particle diameter of the fritglaze thus obtained was measured with a laser diffraction particle sizedistribution analyzer. As a result, it was found that 68% of theparticles were accounted for by particles having a diameter of not morethan 10 μm and the 50% average particle diameter (D50) was 6.0 μm.

Next, the above frit glaze was spray coated onto the same plate specimenas used in Example A1, followed by firing at 1100 to 1200° C. to obtaina sample.

For the sample thus obtained, the surface roughness was measured in thesame manner as in Example A1, and found to be Ra=0.03 μm as measured bythe stylus method and Ra=4.0 nm as measured by AFM.

FIG. 4 shows an enlarged view of the surface obtained using a stylustype surface roughness tester. FIG. 13 shows an enlarged view of thesurface obtained by atomic force microscopy (AFM).

For the sample, tests 1 to 5 described above were carried out. Theresults were as follows.

Test 1: The contact angle with water was 20°.

Test 2: About 25 sec after dropping of water, the Magic Ink was floatedon the surface of water, and, upon inclination of the sample, the MagicInk, together with water, was washed away to entirely remove the MagicInk on the surface of the sample.

Test 3: 20 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: The amount of urinary calculi deposited was smaller than that inComparative Example A1 described below, and a part of the depositedurinary calculi was washed out by running water.

Test 5: The amount of soap soil deposited was smaller than that inComparative Example A1 described below, and soap soil could be removedby rubbing with a water-containing sponge to expose the original surfaceof the glaze layer.

Example A4

The frit glaze (D50=12 μm) (70 parts by weight) obtained in Example A3was mixed with 30 parts by weight of the ball milled frit (D50=1. 2 μm)obtained in Example A1 to obtain a mixed glaze. The particle diameter ofthe mixed glaze thus obtained was measured with a laser diffractionparticle size distribution analyzer. As a result, it was found that 57%of the particles were accounted for by particles having a diameter ofnot more than 10 μm and the 50% average particle diameter (D50) was 6.3μm.

Next, the above glaze was spray coated onto the same plate specimen asused in Example A1, followed by firing at 1100 to 1200° C. to obtain asample.

For the sample thus obtained, the surface roughness was measured in thesame manner as in Example A1, and found to be Ra=0.02 μm as measured bythe stylus method and Ra=4.7 nm as measured by AFM.

Further, for the sample, tests 1 to 5 described above were carried out.The results were as follows.

Test 1: The contact angle with water was 20°.

Test 2: About 20 sec after dropping of water, the Magic Ink was floatedon the surface of water, and, upon inclination of the sample, the MagicInk, together with water, was washed away to entirely remove the MagicInk on the surface of the sample.

Test 3: 20 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: The amount of urinary calculi deposited was smaller than that inComparative Example A1 described below, and a part of the depositedurinary calculi was washed out by running water.

Test 5: The amount of soap soil deposited was smaller than that inComparative Example A1 described below, and soap soil could be removedby rubbing with a water-containing sponge to expose the original surfaceof the glaze layer.

Example A5

A material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 65% of the particles were accounted for by particles having adiameter of not more than 10 μm and the 50% average particle diameter(D50) was 6.2 μm.

Next, the above glaze was spray coated onto the same plate specimen asused in Example A1 to form a lower glaze layer, and the frit glazeprepared in Example A3 was then spray coated thereon to form an upperglaze layer, followed by firing at 1100 to 1200° C. to obtain a sample.

For the sample thus obtained, the surface roughness was measured in thesame manner as in Example A1, and found to be Ra=0.03 μm as measured bythe stylus method and Ra=3.8 nm as measured by AFM.

FIG. 14 shows an enlarged view of the surface obtained by atomic forcemicroscopy (AFM).

Further, for the sample, tests 1 to 5 described above were carried out.The results were as follows.

Test 1: The contact angle with water was 20°.

Test 2: About 20 sec after dropping of water, the Magic Ink was floatedon the surface of water, and, upon inclination of the sample, the MagicInk, together with water, was washed away to entirely remove the MagicInk on the surface of the sample.

Test 3: 20 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: The amount of urinary calculi deposited was smaller than that inComparative Example A1 described below, and a part of the depositedurinary calculi was washed out by running water.

Test 5: The amount of soap soil deposited was smaller than that inComparative Example A1 described below, and soap soil could be removedby rubbing with a water-containing sponge to expose the original surfaceof the glaze layer.

Example A6

A material was provided which had the same composition as the material Afor a glaze except that the ZrO₂ and the pigment were removed from thecomposition of the material A. This material was melted at 1300 to 1450°C. in an electric furnace, and the melt was then quenched in water toobtain a glass frit. The glass frit was then stamp milled. The powderthus obtained (600 g), 400 g of water, and 1 kg of alumina balls wereplaced in a ceramic pot having a volume of 2 liters, and the mixture wasthen ball milled for about 18 hr to obtain a frit glaze. The particlediameter of the frit glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 68% of the particles were accounted for by particles having adiameter of not more than 10 μm and the 50% average particle diameter(D50) was 6.0 μm.

Next, the glaze prepared in Example A5 was spray coated onto the sameplate specimen as used in Example A1 to form a lower glaze layer.Subsequently, the above frit glaze prepared was then spray coatedthereon to form an upper glaze layer, followed by firing at 1100 to1200° C. to obtain a sample.

For the sample thus obtained, the surface roughness was measured in thesame manner as in Example A1, and found to be Ra=0.05 μm as measured bythe stylus method. FIG. 5 shows an enlarged view of the surface obtainedusing a stylus type surface roughness tester.

Further, for the sample, tests 1 to 5 described above were carried out.The results were as follows.

Test 1: The contact angle with water was 16°.

Test 2: About 30 sec after dropping of water, the Magic Ink was floatedon the surface of water, and, upon inclination of the sample, the MagicInk, together with water, was washed away to entirely remove the MagicInk on the surface of the sample.

Test 3: 25 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: The amount of urinary calculi deposited was smaller than that inComparative Example A1 described below, and a part of the depositedurinary calculi was washed out by running water.

Test 5: The amount of soap soil deposited was smaller than that inComparative Example A1 described below, and soap soil could be removedby rubbing with a water-containing sponge to expose the original surfaceof the glaze layer.

Example A7

The frit glaze (D50=6.0 μm) (80 parts by weight) obtained in Example A6was mixed with 20 parts by weight of the glaze (D50=6.5 μm), free fromthe opacefier and the pigment, prepared in Example A2, to obtain a mixedglaze. The particle diameter of the mixed glaze thus obtained wasmeasured with a laser diffraction particle size distribution analyzer.As a result, it was found that 57% of the particles were accounted forby particles having a diameter of not more than 10 μm and the 50%average particle diameter (D50) was 6.3 μm.

Next, the glaze prepared in Example A5 was spray coated onto the sameplate specimen as used in Example A1 to form a lower glaze layer.Subsequently, the above mixed glaze was then spray coated thereon toform an upper glaze layer, followed by firing at 1100 to 1200° C. toobtain a sample.

For the sample thus obtained, the surface roughness was measured in thesame manner as in Example A1, and found to be Ra=0.06 μm as measured bythe stylus method. FIG. 6 shows an enlarged view of the surface obtainedusing a stylus type surface roughness tester.

Further, for the sample, tests 1 to 5 described above were carried out.The results were as follows.

Test 1: The contact angle with water was 19°.

Test 2: About 30 sec after dropping of water, the Magic Ink was floatedon the surface of water, and, upon inclination of the sample, the MagicInk, together with water, was washed away to entirely remove the MagicInk on the surface of the sample.

Test 3: 30 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: The amount of urinary calculi deposited was smaller than that inComparative Example A1 described below, and a part of the depositedurinary calculi was washed out by running water.

Test 5: The amount of soap soil deposited was smaller than that inComparative Example A1 described below, and soap soil could be removedby rubbing with a water-containing sponge to expose the original surfaceof the glaze layer.

Comparative Example A1

The glaze prepared in Example A5 was spray coated onto the same platespecimen as used in Example A1, followed by firing at 1100 to 1200° C.to obtain a sample.

For the sample thus obtained, the surface roughness was measured in thesame manner as in Example A1, and found to be Ra=0.10 μm as measured bythe stylus method and Ra=18.0 nm as measured by AFM.

FIG. 1 shows an enlarged view of the surface obtained using a stylustype surface roughness tester. Further, a concavo-convex image and animage on the composition of the surface were observed under scanningelectron microscope. The concave-convex image of the surface utilizing areflection electron image is shown in FIG. 7(a), and the image on thecomposition of the surface is shown in FIG. 7(b). FIG. 9 is an enlargedview of the surface obtained by observation under an atomic forcemicroscope (AFM).

For the sample, tests 1 to 5 described above were carried out. Theresults were as follows.

Test 1: The contact angle with water was 30°.

Test 2: The Magic Ink was not floated on the surface of water, and, whenthe sample was inclined, it remained on the surface of the sample.

Test 3: 50 sec after submerging, the salad oil was floated on thesurface of water.

Test 4: A large amount of urinary calculi was deposited on the surfaceof the glaze layer of the specimen, and the deposited urinary calculicould not be removed by running water.

Test 5: Soap soil was deposited on substantially the whole surface ofthe glaze layer of the plate specimen, and it was very difficult toremove the soap soil even by rubbing the surface of the plate specimenwith a water-containing sponge.

Comparative Example A2

For a commercially available Western-style toilet (color:ivory), thesurface roughness was measured in the same manner as in Example A1, andfound to be Ra=0.07 μm as measured by the stylus method and Ra=10.4 nmas measured by AFM.

FIG. 2 shows an enlarged view of the surface obtained using a stylustype surface roughness tester. FIG. 10 is an enlarged view of thesurface obtained by observation under an atomic force microscope (AFM).

For the commercially available toilet, tests 1 to 3 described above werecarried out. The results were as follows.

Test 1: The contact angle with water was 50°.

Test 2: After dropping of water, the Magic Ink was not floated on thesurface of water, and, when the sample was inclined, t remained on thesurface of the sample.

Test 3: 120 sec after submerging, the salad oil was floated on thesurface of water.

The results of Example A are summarized in the following Tables 1 and 2.

TABLE 1 Surface roughness Ra Contact angle Stylus type AFM (H₂O) Ex. A10.02 μm  4.3 nm 20° Ex. A2 0.03 μm  3.5 nm 15° Ex. A3 0.03 μm  4.0 nm20° Ex. A4 0.02 μm  4.7 nm 20° Ex. A5 0.03 μm  3.8 nm 20° EX. A6 0.05 μm— 16° Ex. A7 0.06 μm — 19° Comp. Ex. A1 0.10 μm 18.0 nm 30° Comp. Ex. A20.07 μm 10.4 nm 50°

TABLE 2 Time taken for salad Amount of urinary Removability of oil to befloated on calculi deposited on Amount of soap Magic ™ ink waterstrainer in urinal soils on washbowl Ex. A1 No ink left 35 sec SmallSmall Ex. A2 No ink left 15 sec Small Small Ex. A3 No jnk left 20 secSmall Small Ex. A4 No ink left 20 sec Small Small Ex. A5 No ink left 20sec Small Small Ex. A6 No ink left 25 sec Small Small Ex. A7 No ink left30 sec Small Small Comp. Ex. A1 The whole ink left 50 sec Large LargeComp. Ex. A2 The whole ink left 120 sec  — —

Example B Example B1

The material A for a glaze (600 g), 400 g of water, and 1 kg of aluminaballs were placed in a ceramic pot having a volume of 2 liters, and themixture was then ball milled for about 65 hr to obtain a glaze. Theparticle diameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 98% of the particles were accounted for by particles having adiameter of not more than 10 μm and the 50% average particle diameter(D50) was 1.2 μm.

Next, a plate specimen having a size of 70×150 mm was prepared using aslurry for a sanitary ware body obtained using quartz sand, feldspar,clay and the like as raw materials. The glaze was spray coated onto theplate specimen, followed by firing at 1100 to 1200° C. to obtain asample. The color of the glaze in the sample thus obtained was pastelivory (#SC1).

For the sample, the surface roughness and the glossiness were measured.The surface roughness was measured in terms of kurtosis Rku with astylus type surface roughness tester (JIS B 0651), and found to bekurtosis Rku=2.00. The glossiness was measured in terms of specularglossiness at 60° Gs (60°) according to the method of measurement forspecular glossiness (JIS Z 8741), and found to be Gs (60°)=102.0.

Example B2

The material A for a glaze was melted at 1300 to 1450° C. in an electricfurnace, and the melt was then quenched in water to obtain a glass frit.The glass frit was then stamp milled. The powder thus obtained (600 g),400 g of water, and 1 kg of alumina balls were placed in a ceramic pothaving a volume of 2 liters, and the mixture was then ball milled forabout 18 hr to obtain a frit glaze. The particle diameter of the fritglaze thus obtained was measured with a laser diffraction particle sizedistribution analyzer. As a result, it was found that 68% of theparticles were accounted for by particles having a diameter of not morethan 10 μm and the 50% average particle diameter (D50) was 6.0 μm.

Next, the above frit glaze was spray coated onto the same plate specimenas used in Example B1, followed by firing at 1100 to 1200° C. to obtaina sample. The color of the glaze in the sample thus obtained was pastelivory (#SC1).

The sample thus obtained was evaluated in the same manner as in ExampleB1. As a result, the surface roughness in terms of kurtosis Rku was1.90, and the specular glossiness at 60° Gs (60°) was 106.0.

Comparative Example B1

A material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 65% of the particles were accounted for by particles having adiameter of not more than 10 μm and the 50% average particle diameter(D50) was 6.2 μm.

Next, the glaze was spray coated onto the same plate specimen as used inExample B1, followed by firing at 1100 to 1200° C. to obtain a sample.

The color of the glaze in the sample thus obtained was pastel ivory(#SC1).

The sample thus obtained was evaluated in the same manner as in ExampleB1. As a result, the surface roughness in terms of kurtosis Rku was3.04, and the specular glossiness at 60° Gs (60°) was 95.0.

Comparative Example B2

For a commercially available Western-style toilet (color:ivory), thesurface roughness in terms of kurtosis Rku and the specular glossinessat 60° Gs (60°)were measured in the same manner as in Example B1. As aresult, the Rku was 2.70, and Gs (60°) was 98.0.

The results of Example B and Comparative Example B are summarized inFIG. 15. In the figure, A, B, C and D represent the results of ExamplesB1 and B2 and Comparative Examples B1 and B2, respectively. As isapparent from FIG. 15, the glossiness at 60° Gs (60°) increased withdecreasing the surface roughness in terms of kurtosis Rku. That is,there is a negative correlation between the surface roughness and theglossiness. Further, bringing the Rku value to less than 2.70 canprovide a glaze layer surface having a high glossiness Gs (60°) of notless than 100.

Example C

In the following Example C and Comparative Example C, evaluation testswere carried out by the following methods.

Alkali Resistance

A 5% aqueous sodium hydroxide solution was provided. Half of thespecimen was immersed in the aqueous solution. The whole system washeated to 70° C., and allowed to stand at that temperature for 24 hr.Thereafter, the specimen was taken out of the aqueous solution and thenwashed with running water. In this case, the glaze surface before theimmersion and the glaze surface after the immersion were observed undera scanning electron microscope (SEM; S-800, manufactured by Hitachi,Ltd.).

Surface Roughness

The surface roughness was measured with a stylus type surface roughnesstester according to JIS B 0651 in the same manner as in Example A1.

Deposition of Urinary Calculi

Urine collected from a human being was diluted twice with distilledwater. The diluted urine (about 2 liters) was placed in a toilet bowl,followed by sealing. In this state, the sealed toilet bowl was allowedto stand at room temperature for one week. In all the following examplesand comparative examples, the pH value of the urine immediately afterthe dilution and the pH value of the urine after the standing in thetoilet bowl for one week were measured at 25° C. with a pH meter (a pHmeter M-12, manufactured by Horiba, Ltd.), and found to be 6.5 and 8.5,respectively.

The diluted urine within the bowl was disposed of. The inside of thebowl was washed with about 12 liters of running water (corresponding tothe amount of water in washing using conventional flush tanks), and thendried at room temperature. Thereafter, the inside of the bowl wassprayed with a diluted solution of a bacterial plaque staining gel“DENTCLUB,” manufactured by Health Tech Co., Ltd., and the amount ofurine calculus deposited was evaluated based on the depth of red color.Use of the bacterial plaque staining gel permits a portion, where alarge amount of urine calculi has been deposited, to be deeply stainedred, while a portion free from urine calculi is not stained. The amountof urine calculi deposited can be visually evaluated through theutilization of this phenomenon.

Example C

The material A for a glaze was melted at 1400 to 1550° C. in an electricfurnace, and the melt was then quenched in water to obtain a glass frit.The glass frit was then stamp milled. The powder thus obtained (250 g),170 g of water, and 1 kg of balls were placed in a ceramic pot having avolume of 2 liters, and the mixture was then ball milled for about 18 hrto obtain a frit glaze.

Next, a plate specimen having a size of 70×150 mm was prepared using aslurry for a sanitary ware body obtained using quartz sand, feldspar,clay and the like as raw materials. The glaze was spray coated onto theplate specimen, followed by firing at 1100 to 1200° C. to obtain asample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test was very smooth, and were free from silicaparticles. For the glaze surface after the alkali resistance test, therewere dropouts of ZrO₂. Irregularities, however, were small, and thesurface was smooth.

The surface roughness was Ra=0.02 μm before the alkali resistance test,and Ra=0.04 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C1 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C1.

Example C2

A material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 65% of the particles were accounted for by particles having adiameter of not more than 10 μm, the 50% average particle diameter (D50)was 5.8 μm, and the 90% average particle diameter (D90) was 23.3 μm.

Separately, a glaze material was provided which had the same compositionas the material A for a glaze except that ZrO₂ as the emulsifier and thepigment were removed from the composition of the material A. Thismaterial was melted at 1400 to 1550° C. in an electric furnace, and themelt was then quenched in water to obtain a glass frit. The glass fritwas then stamp milled. The powder thus obtained (250 g), 170 g of water,and 1 kg of balls were placed in a ceramic pot having a volume of 2liters, and the mixture was then ball milled for about 18 hr to obtain atransparent frit glaze.

Next, the glaze was spray coated onto the same plate specimen as used inExample C1, and the transparent frit glaze was then spray coatedthereon, followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test and the glaze surface after the test wereobserved under a scanning electron microscope (SEM; S-800, manufacturedby Hitachi, Ltd.). An SEM photograph of the glaze surface before thetest and an SEM photograph of the glaze surface after the test are shownin FIGS. 18 and 19, respectively. These photographs show that the glazesurface before the alkali resistance test is very smooth and free fromsilica particles and that the glaze surface after the alkali resistancetest remains substantially unchanged and is smooth.

The surface roughness was Ra=0.02 μm before the alkali resistance test,and Ra=0.03 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C2 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C2.

Example C3

The material A for a glaze (2 kg), 1 kg of water, and 4 kg of aluminaballs were placed in a ceramic pot having a volume of 6 liters, and themixture was then ball milled for about 36 hr to obtain a glaze. Theparticle diameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 90% of the particles were accounted for by particles having adiameter of not more than 10 μm, the 50% average particle diameter (D50)was 3.3 μm, and the 90% average particle diameter (D90) was 9.9 μm.

Next, the glaze was spray coated onto the same plate specimen as used inExample C1, followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. As comparedwith the sample prepared in Comparative Example C1 below, the glazesurface before the test was smaller in amount and size of silicaparticles, was free from silica particles having a size of not less than10 μm, and was very smooth. The glaze surface after the alkaliresistance test was very small in the number of cracks, and was smooth.

The surface roughness was Ra=0.03 μm before the alkali resistance test,and Ra=0.10 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C1 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C1.

Example C4

The material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 65% of the particles were accounted for by particles having adiameter of not more than 10 μm, the 50% average particle diameter (D50)was 5.8 μm, and the 90% average particle diameter (D90) was 23.3 μm.

Separately, a material was provided which had the same composition asthe material A for a glaze except that ZrO₂ as the emulsifier and thepigment were removed from the composition of the material A. Thismaterial (2 kg), 1 kg of water, and 4 kg of alumina balls were placed ina ceramic pot having a volume of 6 liters, and the mixture was then ballmilled for about 60 hr to obtain a milled transparent glaze. For themilled transparent glaze, 100% of the particles were accounted for byparticles having a diameter of not more than 10 μm, the D50 value was1.7 μm, and the D90 value was 3.8 μm.

Next, the glaze was spray coated onto the same plate specimen as used inExample C1, and the milled transparent glaze was then spray coatedthereon, followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test was very smooth and free from silica particles.The glaze surface after the alkali resistance test remainedsubstantially unchanged and was smooth.

The surface roughness was Ra=0.03 μm before the alkali resistance test,and Ra=0.04 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C2 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C2.

Example C5

The material was provided which had the same composition as the materialA for a glaze except that quartz sand as the raw material of silicaparticles and the commercially available feldspar material were removedfrom the composition of the material A. This material (2 kg), 1 kg ofwater, and 4 kg of alumina balls were placed in a ceramic pot having avolume of 6 liters, and the mixture was then ball milled for about 18 hrto obtain a glaze. The particle diameter of the glaze thus obtained wasmeasured with a laser diffraction particle size distribution analyzer.As a result, it was found that 99% of the particles were accounted forby particles having a diameter of not more than 10 μm, the 50% averageparticle diameter (D50) was 2.2 μm, and the 90% average particlediameter (D90) was 5.1 μm.

Separately, 400 g of quartz sand, 200 g of commercially availablefeldspar material, 300 g of water, and 1.2 kg of alumina balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 40 hr to obtain a silica slurry. For thesilica slurry, 98% of the particles were accounted for by particleshaving a diameter of not more than 10 μm, the D50 value was 2.4 μm, andthe D90 value was 5.5 μm.

The glaze and the silica slurry were mixed together in a weight ratio of4:6 to obtain a mixed glaze. For the mixture glaze, 99% of the particleswere accounted for by particles having a diameter of not more than 10μm, the D50 value was 2.3 μm, and the D90 value was 5.3 μm.

Next, the mixed glaze was spray coated onto the same plate specimen asused in Example C1, followed by firing at 1100 to 1200° C. to obtain asample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test was very smooth and free from silica particleshaving a size of more than 10 μm. The glaze surface after the alkaliresistance test remained substantially unchanged and was smooth,although a very small amount of cracked silica particles having a sizeof not more than 10 μm were present.

The surface roughness was Ra=0.04 μm before the alkali resistance test,and Ra=0.11 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C1 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C1.

Example C6

The material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the ball milled glaze thus obtained was measured with alaser diffraction particle size distribution analyzer. As a result, itwas found that 65% of the particles were accounted for by particleshaving a diameter of not more than 10 μm, the 50% average particlediameter (D50) was 5.8 μm, and the 90% average particle diameter (D90)was 23.3 μm.

Separately, a glaze material was provided which had the same compositionas the material A for a glaze except that ZrO₂ as the emulsifier, thepigment, the quartz sand as the raw material for silica particles, andthe commercially available feldspar material were removed from thecomposition of the material A. This material (2 kg), 1 kg of water, and4 kg of alumina balls were placed in a ceramic pot having a volume of 6liters, and the mixture was then ball milled for about 18 hr to obtain atransparent glaze. For the transparent glaze, 97% of the particles wereaccounted for by particles having a diameter of not more than 10 μm, theD50 value was 2.3 μm, and the D90 value was 5.0 μm.

Further, separately, 400 g of quartz sand, 200 g of feldspar, 300 g ofwater, and 1.2 kg of alumina balls were placed in a ceramic pot having avolume of 6 liters, and the mixture was then ball milled for about 40 hrto obtain a silica slurry. For the silica slurry, 98% of the particleswere accounted for by particles having a diameter of not more than 10μm, the D50 value was 2.4 μm, and the D90 value was 5.5 μm.

The transparent glaze and the silica slurry were mixed together in aweight ratio of 4:6 to obtain a transparent mixed glaze. For thetransparent mixed glaze, 98% of the particles were accounted for byparticles having a diameter of not more than 10 μm, the D50 value was2.4 μm, and the D90 value was 5.3 μm.

Next, the glaze was spray coated onto the same plate specimen as used inExample C1, and the transparent mixed glaze was then spray coatedthereon, followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test was very smooth and free from silica particleshaving a size of more than 10 μm. The glaze surface after the alkaliresistance test remained substantially unchanged from the state beforethe test and was smooth, although a very small amount of cracked silicaparticles having a size of not more than 10 μm were present.

The surface roughness was Ra=0.04 μm before the alkali resistance test,and Ra=0.05 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C2 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C2.

Example C7

The material A for a glaze was melted at 1400 to 1550° C. in an electricfurnace, and the melt was then quenched in water to obtain a glass frit.The glass frit was then stamp milled. The powder thus obtained (250 g),170 g of water, and 1 kg of balls were placed in a ceramic pot having avolume of 2 liters, and the mixture was then ball milled for about 18 hrto obtain a frit glaze.

Separately, 2 kg of the material A for a glaze, 1 kg of water, and 4 kgof alumina balls were placed in a ceramic pot having a volume of 6liters, and the mixture was then ball milled for about 36 hr to obtain amilled glaze. For the milled glaze, 90% of the particles were accountedfor by particles having a diameter of not more than 10 μm, the D50 valuewas 3.3 μm, and the D90 value was 9.9 μm.

The frit glaze and the milled glaze were mixed together in a weightratio of 8:2 to obtain a mixed glaze. For the mixed glaze, 76% of theparticles were accounted for by particles having a diameter of not morethan 10 μm, the D50 value was 4.0 μm, and the D90 value was 15.9 μm.

Next, the mixed glaze was spray coated onto the same plate specimen asused in Example C1, followed by firing at 1100 to 1200° C. to obtain asample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test was very smooth and free from silica particleshaving a size of more than 10 μm. As compared with the sample preparedin Comparative Example C1 below, the glaze surface before the test wassmaller in the number and size of silica particles. The glaze surfaceafter the alkali resistance test was small in the number of crackscreated around silica particles, remained substantially unchanged fromthe glaze surface before the test, and was smooth.

The surface roughness was Ra=0.05 μm before the alkali resistance test,and Ra=0.10 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C1 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C1.

Example C8

The material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the glaze obtained after the ball milling was measured witha laser diffraction particle size distribution analyzer. As a result, itwas found that 65% of the particles were accounted for by particleshaving a diameter of not more than 10 μm, the 50% average particlediameter (D50) was 5.8 μm, and the 90% average particle diameter (D90)was 23.3 μm.

Separately, a glaze material for a glaze was provided which had the samecomposition as the material A for a glaze except that ZrO₂ as theemulsifier and the pigment were removed from the composition of thematerial A. This material was melted at 1400 to 1550° C. in an electricfurnace, and the melt was then quenched in water to obtain a glass frit.The glass frit was then stamp milled. The powder thus obtained (1.6 kg),0.4 kg of a material for a glaze having the same composition as thematerial A for a glaze except that ZrO₂ as the emulsifier and thepigment were removed from the composition of the material A, 1 kg ofwater, and 4 kg of balls were placed in a ceramic pot having a volume of6 liters, and the mixture was then ball milled for about 36 hr to obtaina transparent mixed glaze.

Next, the glaze was spray coated onto the same plate specimen as used inExample C1, and the transparent mixed glaze was spray coated thereon,followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test was very smooth and free from silica particleshaving a size of more than 10 μm. As compared with the sample preparedin Comparative Example C2 below, the glaze surface before the test wassmaller in the number and size of silica particles. The glaze surfaceafter the alkali resistance test was small in the number of crackscreated around silica particles, remained substantially unchanged fromthe glaze surface before the test, and was smooth.

The surface roughness was Ra=0.04 μm before the alkali resistance test,and Ra=0.06 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, werelightly stained red. This depth of red was clearly smaller than that ofred in Comparative Example C2 below, indicating that the amount of urinecalculi deposited was smaller than that in Comparative Example C2.

Comparative Example C1

The material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the glaze obtained after the ball milling was measured witha laser diffraction particle size distribution analyzer. As a result, itwas found that 65% of the particles were accounted for by particleshaving a diameter of not more than 10 μm, the 50% average particlediameter (D50) was 5.8 μm, and the 90% average particle diameter (D90)was 23.3 μm.

Separately, 1.2 kg of quartz sand incorporated as an SiO₂ source intothe material A for a glaze and 0.8 kg of a commercially availablefeldspar material, together with 1 kg of water and 4 kg of balls, wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr. For the ball milled product, the D50value was 9.3 μm. This suggests that the quartz sand and thecommercially available feldspar material in the glaze have been milledto a D50 value around 10 μm.

Next, the glaze was spray coated onto the same plate specimen as used inExample C1, followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. The glazesurface before the test and the glaze surface after the test wereobserved under a scanning electron microscope (SEM; S-800, manufacturedby Hitachi, Ltd.). The glaze surface before the alkali resistance testhad concaves due to the presence of a large number of silica particles.For the glaze surface after the alkali resistance test, cracks werecreated around the silica particles, and there were dropouts of thesilica particles, resulting in increased size of irregularities.

The surface roughness was Ra=0.10 μm before the alkali resistance test,and Ra=0.25 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, within thebowl were deeply stained red, indicating that a large amount of urinecalculi was deposited.

Comparative Example C2

The material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the glaze obtained after the ball milling was measured witha laser diffraction particle size distribution analyzer. As a result, itwas found that 65% of the particles were accounted for by particleshaving a diameter of not more than 10 μm, the 50% average particlediameter (D50) was 5.8 μm, and the 90% average particle diameter (D90)was 23.3 μm.

Separately, a material was provided which had the same composition asthe material A for a glaze except that ZrO₂ as the emulsifier and thepigment were removed from the composition of the material A. Thismaterial (2 kg), 1 kg of water, and 4 kg of balls were placed in aceramic pot having a volume of 6 liters, and the mixture was then ballmilled for about 18 hr to obtain a transparent glaze. For thetransparent glaze, 63% of the particles were accounted for by particleshaving a diameter of not more than 10 μm, the D50 value was 6.0 μm, andthe D90 value was 25.4 μm.

Next, the glaze was spray coated onto the same plate specimen as used inExample C1, and the transparent glaze was then spray coated thereon,followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. An SEMphotograph of the glaze surface before the test and an SEM photograph ofthe glaze surface after the test are shown in FIGS. 16 and 17,respectively. As can be seen from these photographs, the glaze surfacebefore the alkali resistance test had concaves attributable to thepresence of a large number of silica particles (deeply dark portion).For the glaze surface after the alkali resistance test, cracks werecreated around the silica particles, and there were dropouts of thesilica particles, resulting in increased size of irregularities.

The surface roughness was Ra=0.08 μm before the alkali resistance test,and Ra=0.10 μm after the alkali resistance test.

A toilet bowl was prepared in the same manner as used in connection withthe preparation of the sample described above. The toilet bowl thusobtained was tested for the deposition of urine calculi. The inside ofthe bowl was sprayed with a diluted solution of a bacterial plaquestaining gel. As a result, a portion, which had drawn the diluted urine,and a portion, which had been immersed in the diluted urine, within thebowl were deeply stained red, indicating that a large amount of urinecalculi was deposited.

Example D

Examples D1 to D6 and Comparative Examples D1 to D5 The material A for aglaze (2 kg), 1 kg of water, and 4 kg of balls were placed in a ceramicpot having a volume of 6 liters, and the mixture was then ball milledfor about 18 hr to obtain a color glaze. The particle diameter of thecolor glaze thus obtained was measured with a laser diffraction particlesize distribution analyzer. As a result, it was found that 65% of theparticles were accounted for by particles having a diameter of not morethan 10 μm and the 50% average particle diameter (D50) was 5.8 μm.

Separately, a material for a glaze was provided which had the samecomposition as the material A for a glaze except that ZrO₂ as theemulsifier and the pigment were removed from the composition of thematerial A. This material was melted at 1300 to 1500° C. in an electricfurnace, and the melt was then quenched in water to obtain a glass frit.A material for a glaze having the same composition as the material A fora glaze except that ZrO₂ as the emulsifier and the pigment were removedfrom the composition of the material A, the frit glaze, water, and ballswere placed in a ceramic pot, and the mixture was ball milled until64±2% of the particles were accounted for by particles having a diameterof not more than 10 μm. Thus, a transparent mixed glaze was obtained.The mixing ratio of the material for a glaze to the frit glaze in thetransparent mixed glaze were as indicated in the following table.

Next, a plate specimen having a size of 70×150 mm was prepared using aslurry for a sanitary ware body obtained using quartz sand, feldspar,clay and the like as raw materials. The color glaze was spray coatedonto the plate specimen, and the transparent mixed glaze was spraycoated thereon, followed by firing at 1100 to 1200° C. to obtain asample.

The samples thus obtained were tested for alkali resistance in the samemanner as in Example C. The surface of the glaze layer before the alkaliresistance test in Example D4 (glaze material frit glaze=20:80) is shownin FIG. 22. The surface free from the emulsifier and substantially freefrom silica particles was much smoother than the surface of the glazelayer before the alkali resistance test in Comparative Example D6described below. For the other samples, the higher the proportion of thefrit glaze, the lower the amount of silica particles and the smootherthe surface. The surface of the glaze layer after the alkali resistancetest in Example D4 is shown in FIG. 23. As can be seen from FIG. 23, thesurface had no irregularities attributable to dropouts of silicaparticles, and remained smooth. For the other samples, the higher theproportion of the frit glaze, the smaller the number of cracks createdaround the silica particles and the better the smoothness.

For the samples, the surface roughness Ra was as shown in the followingtable.

Further, for the samples, the glossiness of the surface before and afterthe alkali resistance test was measured with a gloss meter (GM-060,manufactured by Minolta) to determine gloss retention defined by thefollowing equation:

Gloss retention (%)=(“glossiness after alkali resistancetest”/“glossiness before alkali resistance test”)×100

The results are summarized in the following table.

Toilet bowls were prepared in the same manner as described above inconnection with the preparation of the samples. The toilet bowls thusobtained were tested for the deposition of urine calculi in the samemanner as in Example C. The results were as shown in the followingtable. In the table, ∘ represents that the amount of urine calculideposited was much smaller than that in Comparative Example D6 describedbelow; X represents that the amount of urine calculi deposited wasrelatively large although the amount was smaller than that inComparative Example D6 described below; and - represents that the testwas not carried out.

TABLE 3 Mixing proportion, wt % Surface roughness Ra, μm Gloss GlazeFrit Before alkali After alkali retention, Deposition of material glazeresistance test resistance test % urine calculi Ex. D1 50 50 0.067 0.10991.4 ◯ Ex. D2 40 60 0.054 0.098 92.1 ◯ Ex. D3 30 70 0.057 0.082 93.9 —Ex. D4 20 80 0.047 0.065 95.6 ◯ Ex. D5 10 90 0.038 0.054 97.5 — Ex. D6 0100 0.029 0.037 100 ◯ Comp. Ex. D1 100 0 0.081 0.137 81.2 X Comp. Ex. D290 10 0.090 0.147 81.6 — Comp. Ex. D3 80 20 0.088 0.139 82.0 X Comp. Ex.D4 70 30 0.083 0.135 82.9 — Comp. Ex. D5 60 40 0.079 0.129 85.8 X

Comparative Example D6

The material A for a glaze (2 kg), 1 kg of water, and 4 kg of balls wereplaced in a ceramic pot having a volume of 6 liters, and the mixture wasthen ball milled for about 18 hr to obtain a glaze. The particlediameter of the color glaze thus obtained was measured with a laserdiffraction particle size distribution analyzer. As a result, it wasfound that 65% of the particles were accounted for by particles having adiameter of not more than 10 μm and the 50% average particle diameter(D50) was 5.8 μm.

Next, the glaze was spray coated onto the plate specimen as used inExample D, followed by firing at 1100 to 1200° C. to obtain a sample.

The sample thus obtained was tested for alkali resistance. A scanningmicrophotograph of the glaze surface before the test is shown in FIG.20. As can be seen from the microphotograph, the emulsifier (whiteportion) and the silica particles (deeply dark portion) were present andconstituted irregularities. A scanning microphotograph of the glazesurface after the test is shown in FIG. 21. A scan be seen from themicrophotograph, cracks were created around the silica particles, andthere were dropouts of the silica particles, resulting in increased sizeof irregularities.

For the sample, the surface roughness was Ra=0.10 μm before the alkaliresistance test, and Ra=0.25 μm after the alkali resistance test.

The glossiness was measured in the same manner as in Example D. As aresult, the glossiness after the test was less than 50% of theglossiness before the test, that is, the gloss retention was 43.2%.

Further, a urine calculi deposition test was carried out in the samemanner as in Examples D1 to D6. As a result, a large amount of urinecalculi was deposited, and the urine calculi could not be removed byrunning water.

What is claimed is:
 1. A sanitary ware comprising: a sanitary ware body;and a surface glaze layer formed by applying a particulate glazematerial having a 50% particle diameter of not more than 4 μm onto asurface of the sanitary ware body to form a precursor layer and thenfiring the precursor layer to convert the precursor layer to the surfaceglaze layer.
 2. The sanitary ware of claim 1 wherein the surface glazelayer has a center line average roughness Ra of less than 0.07 μm asmeasured with a stylus type surface roughness tester according to JIS B0651-1996.
 3. The sanitary ware of claim 2 wherein the Ra is not morethan 0.03 μm.
 4. The sanitary ware of any one of claims 1 to 3 whereinthe surface glaze layer is absent on a part of the surface of thesanitary ware body.
 5. The sanitary ware of claim 1 wherein at least oneglaze layer is provided between the sanitary ware body and the surfaceglaze layer.
 6. The sanitary ware of claim 5 wherein the surface glazelayer is absent on a part of the surface of the surface of the sanitarywe body.
 7. The sanitary ware of claim 1 wherein the surface glaze layerhas a contact angle with water of less than 30°.
 8. The sanitary ware ofclaim 7 wherein the contact angle is not more than 25°.
 9. The sanitaryware of claim 7 wherein the contact angle is not more than 20°.
 10. Thesanitary ware of claim 1 wherein the sanitary ware is a strainer forurinals, a toilet, a urinal, a flush tank for toilets or urinals, awashbowl in a washstand, or a wash hand basin.
 11. The sanitary ware ofclaim 1 wherein the sanitary ware is a toilet or a urinal, the surfaceglaze layer being provided at least on the surface of a bowl of thetoilet or the urinal, the surface glaze layer being absent on a part ofthe surface of the toilet or the urinal.
 12. The sanitary ware of claim1 wherein the particulate glaze material is an amorphous glaze material.13. The sanitary ware of claim 12 wherein the amorphous glaze materialis a vitrified frit glaze material.
 14. The sanitary ware of claim 1wherein the glaze material is a mixed glaze comprised of an amorphousglaze material and non-frit glaze material.
 15. The sanitary ware ofclaim 14 wherein the amorphous glaze material is a vitrified frit glazematerial.
 16. The sanitary ware of claim 14 or 15 wherein the non-fritglaze material has been subjected to size reduction.
 17. The sanitaryware of claim 1 wherein at least one color glaze layer is providedbetween the sanitary ware body and the surface glaze layer, and thesurface glaze layer is transparent.
 18. The sanitary ware of claim 17wherein the particulate glaze material has a 50% particle diameter ofnot more than 1.5 μm.
 19. The sanitary ware of claim 17 wherein theparticulate glaze material is an amorphous glaze material.
 20. Thesanitary ware of claim 19 wherein the amorphous glaze material is avitrified frit glaze material.
 21. The sanitary ware of claim 17 whereinthe particulate glaze material is a mixed glaze comprised of anamorphous glaze material and a non-frit glaze material.
 22. The sanitaryware of claim 21 wherein the amorphous glaze material is a vitrifiedfrit glaze material.
 23. The sanitary ware of claim 1 wherein theparticulate glaze material has a 50% particle,diameter of not more than1.5 μm.
 24. The sanitary ware of claim 1 wherein the surface glaze layerhas a kurtosis Rku of less than 2.70.
 25. The sanitary ware of claim 24wherein the kurtosis Rku is not more than 2.60.
 26. The sanitary ware ofclaim 24 wherein the kurtosis Rku is not more than 2.50.
 27. Thesanitary ware of claim 1 herein the surface glaze layer consistsessentially of a vitreous component and is free from silica particleshaving a particle diameter of not less than 10 μm after firing thesurface glaze layer.
 28. The sanitary ware of claim 27 wherein the wholesurface glaze layer consists essentially of a vitreous component. 29.The sanitary ware of claim 27 or 28 wherein the surface glaze layer isfree from a pigment.
 30. The sanitary ware of claim 27 or 28 wherein thesurface glaze layer contains a pigment.
 31. A sanitary ware of claim 27wherein the firing is at a temperature of 1300° C. or below.
 32. Thesanitary ware of claim 31 wherein the temperature is 1100-1300° C.
 33. Aprocess for making the sanitary ware of claim 1, the process comprising:applying a particulate glaze material having a 50% particle diameter ofnot more than 4 μm onto a sanitary ware body to form a precursor layer;and firing the precursor layer to convert the precursor layer to thesurface glaze layer.